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Mol Cancer Res. 2009 Oct;7(10):1693-703. doi: 10.1158/1541-7786.MCR-09-0031. Epub 2009 Oct 13.

PU.1 activation relieves GATA-1-mediated repression of Cebpa and Cbfb during leukemia differentiation.

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Institute of Pathological Physiology and Center of Experimental Hematology, First Faculty of Medicine, Charles University in Prague, Prague, Czech Republic.


Hematopoietic transcription factors GATA-1 and PU.1 bind each other on DNA to block transcriptional programs of undesired lineage during hematopoietic commitment. Murine erythroleukemia (MEL) cells that coexpress GATA-1 and PU.1 are blocked at the blast stage but respond to molecular removal (downregulation) of PU.1 or addition (upregulation) of GATA-1 by inducing terminal erythroid differentiation. To test whether GATA-1 blocks PU.1 in MEL cells, we have conditionally activated a transgenic PU.1 protein fused with the estrogen receptor ligand-binding domain (PUER), resulting in activation of a myeloid transcriptional program. Gene expression arrays identified components of the PU.1-dependent transcriptome negatively regulated by GATA-1 in MEL cells, including CCAAT/enhancer binding protein alpha (Cebpa) and core-binding factor, beta subunit (Cbfb), which encode two key hematopoietic transcription factors. Inhibition of GATA-1 by small interfering RNA resulted in derepression of PU.1 target genes. Chromatin immunoprecipitation and reporter assays identified PU.1 motif sequences near Cebpa and Cbfb that are co-occupied by PU.1 and GATA-1 in the leukemic blasts. Significant derepression of Cebpa and Cbfb is achieved in MEL cells by either activation of PU.1 or knockdown of GATA-1. Furthermore, transcriptional regulation of these loci by manipulating the levels of PU.1 and GATA-1 involves quantitative increases in a transcriptionally active chromatin mark: acetylation of histone H3K9. Collectively, we show that either activation of PU.1 or inhibition of GATA-1 efficiently reverses the transcriptional block imposed by GATA-1 and leads to the activation of a myeloid transcriptional program directed by PU.1.

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